The present invention relates to photovoltaics (PV) and more specifically to concentrator photovoltaic modules and methods for making same.
The scientific community has been active in the area of photovoltaics (generation of electricity from sunlight) since the early 1960's. Initial application of this technology was directed towards uses as power sources for unmanned spacecraft. With great success in this area, the emphasis shifted to terrestrial applications. It was recognized that there was great potential in a technology that provided energy without some of the pollution drawbacks and depletion of non-renewable resources that are inherent in traditional energy generation sources.
With emphasis provided by the energy crisis of the seventies and monetary support from government sponsored programs, the pace of research and improvements in photovoltaic (PV) efficiency accelerated rapidly into the early 1980's. When the efficiency of PV reached the range of 11 to 13 percent, gains became more difficult to acquire and the associated costs of PV were becoming more apparent. By mid-1980, the cost of installed PV was still around $9.00/peak watt and of this the PV module cost was about $5.50. These figures were far above the Department of Energy (DOE) estimates of $0.50/peak watt required for PV to be competitive with existing energy sources.
The two most common methods of deploying solar cells is in a flat plate configuration, and in concentrating collector designs. The flat plate design is comprised of an assembly of solar cells arranged in a tightly packed configuration and grouped to make modules that range in sizes of one foot square to units as large as ten feet square. The flat plate collectors utilize the sun's energy on a one to one basis, meaning that all areas of the individual solar cells are exposed to an energy input equivalent of one sun radiation (minus any optical losses associated with protective cover glasses and reflection). These modules are stationary, mounted facing south, or often they are mounted on sun tracking units to increase solar input up to 30 percent. The major cost of the flat plate collector is the solar cell itself; about 55 percent of the finished module cost. Since the power output is determined by the area coverage of the cells, there are not many options to reduce the costs in this configuration except to use cheaper PV base materials. Many organizations are now investigating thin film technologies in an effort to break this price barrier.
The other approach, concentrating PV collectors, makes use of lenses or other refracting devices to focus sunlight onto specific areas of cell material to reduce the amount of expensive PV material required for a given power output. Conventionally, these concentrating collectors use large lenses (fresnel or variations thereof) to concentrate the sun's energy. The result of this is that the focal length lens is long, requiring massive support structures and, consequently, matching tracking devices. The net result is a cost that is certainly competitive with but not more cost effective that flat-plate technology.
The solution of the present invention to these immovable cost barriers is to combine the best of both technologies. The invention involves the use of small lens elements concentrating onto small solar cells. With lenses approximately one-half inch square and crystals approximately one-eighth inch square, the cost of the PV material is reduced by a factor of 15 with a module thickness of less than one inch. These two factors substantially reduce the overall costs of producing PV modules. The other non-obvious result of this approach is the compatability of producing these modules with automated production techniques. The small cells can be located and easily soldered in place with robot type equipment eliminating much of the hand assembly of current products. The combination of these factors makes the present invention capable of being produced by fully automated processes for a relatively low cost.
In addition, to breaking the cost barrier, the small size and particular arrangement of the components of the present invention results in a high efficiency electrical power source which uses concentrating collectors but does not require auxiliary cooling.
In my U.S. Pat. No. 4,638,110 for METHODS AND APPARATUS RELATING TO PHOTOVOLTAIC SEMICONDUCTOR DEVICES issued Jan. 20, 1987, I describe a photovoltaic power module characterized by an extreme reduction in scale wherein the photovoltaic crystals are formed in situ and affixed directly to a lens sheet onto which has been formed an array of micro sized miniature lenses which concentrate and direct sunlight onto the micro photovoltaic crystals. By using crystals of extremely small dimensions, the distances traveled by both migrating electrons and heat generated within the crystal are small thus eliminating the major factors responsible for limiting the power generating efficiency well known in photovoltaic devices of conventional dimensions. Because of the heat dissipating characteristics of small crystals, it is possible with my invention to employ concentrating lenses magnifying the incident radiation by 40 or 50 times without creating the necessity of employing external cooling devices.
The present invention similarly utilizes small scale components to form a photovoltaic power module including concentrating lenses which does not require auxiliary heat dissipating equipment in order to maintain an operating temperature at which the module can produce power efficiently.
In the present invention, the individual module components are of a scale larger than that taught in my previously identified patent making it possible to employ pre-fabricated cell elements which can be handled along with the other components of the module by existing automated production equipment and techniques so as to reduce the manufacturing cost. Accordingly, the present invention is capable of being produced and operated at low per watt costs making it an attractive alternative to fossil fuel power generating sources.